My Observations

Easy To Upgrade

As with Maverick betas, the Yosemite betas are easy to upgrade over the air using the standard method to upgrade OS X via the Mac App Store app under Updates.

The download is just over 1GB. On my MacBook Air the install process took less than 20 minutes.

Faster and More Stable

So far Yosemite Dev Preview 2 is faster. They've added back the Photo Booth app. Mail is more stable, but I did encounter a crash after time it started. Checking out the report generated by the crash, I discovered that it was caused by an offline Google Mail account. Removing the account fixed the issue, and Mail hasn't crashed on me all day since removing that offline account.

VMware Fusion Still Does Not Work

VMware Fusion v6.0.3 still will not run on a Yosemite host with Dev Preview 2. No surprise there as this is an issue with VMware itself. VMware will have to fix that one.

I hope they fix it soon, but I'm not holding my breathe because they didn't update Fusion until after Mavericks was released, and they required existing VMware Fusion v5 owners to purchase VMware Fusion v6 at the upgrade price. Fusion v5 was never updated to officially support the released version of Mavericks, although it did work as a host OS and guest OS. So I'm expecting to have to fork over more bucks again to VMware for a Fusion upgrade in the fall after Yosemite is officially released.

New Features

Here are some links to some great articles on Yosemite features - listed in the order I suggest you read them: